JP2767823B2 - Automatic platen gap adjustment device for printer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a technique for automatically adjusting a platen gap to an optimum value by detecting a thickness of a printing paper.

(Prior art) In a printer of a wire dot type or a thermal transfer type, since the print density changes depending on the gap length between the print head and the print paper, the thickness of the print paper is usually detected, and the print head is mounted based on this detection signal. The distance between the print head and the platen, that is, the so-called platen gap is adjusted by moving the carriage.

That is, as shown in Japanese Patent Application Laid-Open No. 60-234872, a pressure-sensitive element is fixed to a carriage movably provided in a direction perpendicular to a platen, and the thickness of a sheet is detected as an electric signal. One that automatically adjusts the platen gap based on this signal has been proposed.

(Problem to be Solved) In this apparatus, when detecting the thickness of the printing paper, it is necessary to move the carriage vertically, so that not only the response speed is low, but also the relative distance to the platen varies. Since the measurement is performed via the carriage, a measurement error may occur in the process of detecting the sheet thickness, and there is a problem that the reliability of the adjustment of the platen gap is low.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a platen gap adjustment device capable of adjusting the thickness of a printing paper reliably and at a high speed. is there.

(Means for Solving the Problems) In order to solve such a problem, in the present invention,
While guiding the carriage parallel to the platen,
In a base provided with a carriage guide shaft for adjusting a relative gap with a platen, the base is pivotally supported by a shaft provided on the base, one end of which can abut on the platen, and is always separated from the platen. A lever member urged to move, a displacement detecting means provided on the base for detecting a displacement amount of the other end of the lever member, and controlling the carriage guide shaft by a signal from the displacement detecting means. Means were provided.

(Operation) The thickness of the paper can be detected based on the base on which the platen is fixed, and the displacement magnification can be freely adjusted by adjusting the rotation fulcrum of the lever member. Adjust if possible.

(Embodiment) Therefore, the details of the present invention will be described below based on an illustrated embodiment.

FIG. 1 shows an embodiment of the present invention. In the drawing, reference numeral 1 denotes a platen, which is rotatably provided on left and right frames 5 and 6 forming a printer base. The carriage 2 is connected to the paper feed motor 2 via a transmission gear 4, and a carriage guide shaft 7 is disposed in front of the motor 2 in parallel with the platen 1. This carriage guide shaft 7
Is rotatably attached to the through holes 8 and 9 in an eccentric state,
A platen gap adjusting gear 12 is fixed to one end, and is connected to a gap adjusting motor 13 via a driving gear 10 and a transmission gear 11. A position detection plate 14 for converting the amount of rotation of the gear 12 into a light amount is fixed to a side surface of the platen adjustment gear 12, and a light emitting element for converting the amount of rotation of the detection plate 14 into an electric signal is provided on the base side. Photo sensor 15 consisting of light receiving element
Are arranged.

Reference numeral 16 denotes a carriage on which a print head 17 is mounted. The carriage 16 is supported by the guide shaft 7 and a second guide shaft 18 parallel to the guide shaft 7, and is stretched between a pinion gear 22 of a carriage drive motor 21 and an idle roller 24. While being reciprocated in the direction of the platen axis by the timing belt 23, it is also configured to be movable in the direction perpendicular to the platen 1 by the rotation of the guide shaft 7.

Reference numeral 20 denotes a sheet thickness detection mechanism attached to the base 33, and reference numeral 28 in the figure denotes a sheet thickness detection lever, which is rotatably attached to the base by a shaft 29 and is always connected to the platen 1 by a spring 35. It is provided so as to maintain a separated state, has a leading end protruding from a window of the paper guide plate 25, and has a rear end attached to a plunger 32 driven by a solenoid 30 via a shaft 31. At the rear end side of the sheet thickness detection lever 38, a displacement detector 20, which will be described later, is provided.

FIG. 3 shows an embodiment of the above-mentioned paper thickness detecting mechanism 20. In the drawing, reference numeral 37 denotes a pressure-sensitive element made of a pressure-sensitive conductive rubber whose electric resistance is changed by an externally applied pressure. One surface is fixed to the frame 40 via a protection plate 39 also serving as an electrode, and the other surface is configured to contact the pressing portion 36 of the sheet thickness detection lever 28 via the protection plate 38. I have. The reference numeral 27 in the figure indicates the lever 26
Is a paper detector that operates via the.

FIG. 4 shows an embodiment of a platen gap control circuit, wherein reference numerals 45 and 46 denote paper thickness detection mechanisms 20.
A storage circuit 47 for storing the first signal and the second signal from the pressure-sensitive element 37 is a CPU that controls the platen gap adjustment operation.
Thus, signals from the sheet detector 27 and the signal storage circuits 45 and 46 are input, and the motors 2 and 13 and the solenoid 30 are controlled based on a flowchart described later.

Next, the operation of the device configured as described above will be described based on the flowchart shown in FIG.

[Initial adjustment] At the stage where assembly is completed, the platen 1
The eccentric guide shaft 7 is rotated so that the gap between the print head 17 and the carriage 16 becomes a reference value. In this state, the photo sensor 15 and the position detection plate 14 are relatively moved to adjust the print head 17 to a fixed gap length with respect to the surface of the platen 1, and this is set as a reference position.

At this position, the solenoid 30 is urged to pull the sheet thickness detection lever 28, and the contact portion 34 at the tip of the lever is brought into contact with the surface of the platen 1. As a result, the pressure-sensitive element 37 is pressed by the pressing portion 36 with a pressure proportional to the distance between the contact portion 34 of the lever 28 and the surface of the platen 1, and the displacement detector 20 outputs an electric signal. This electric signal is input to the storage circuit 45 and stored as an initial value.

[Platen Gap Adjustment Operation] When the printer is turned on to perform printing (a), the motor 13 operates to rotate the eccentric guide shaft 7 to move the carriage 17 perpendicular to the surface of the platen 1. In this way, when the print head 17 moves to a position where the reference gap length Gs is reached with respect to the platen surface, the reference position detection plate 14 reaches the reference position, and a signal is output from the photo sensor 15 to rotate the motor 13. Stops (b).

In this state, when the printing paper is inserted along the paper guide 25, the detection lever 26 is pushed down, and the paper detector 27 outputs a paper detection signal (c). This signal causes CPU4
7 excites the solenoid 30 to press the contact portion 34 of the detection lever 28 against the surface of the platen 1 (d). As a result, the pressure signal when there is no paper, that is, the reference gap length Gs
Is output and stored in the storage circuit 45 (e).

When the initial signal is output, the solenoid 30 is deenergized to release the pressure contact of the detection lever 28 with the platen surface, and then the print paper feed motor 2 is operated to move the print paper P to the initial print position. .

When the printing paper is set at the initial printing position (f), the CPU 47 excites the solenoid 30 again and presses the contact portion 34 of the detection lever 28 against the platen 1 (g). In this case, since the printing paper is present on the platen surface, the abutting portion 34 of the lever 28 is in a state of being raised toward the displacement detection mechanism 20 by the thickness ΔD of the printing paper as compared with the case where no paper is present, The corresponding second signal E2 is output and stored in the second signal storage circuit 46 (h).

Since the difference E2−E1 between the second signal and the first signal represents the thickness ΔD of the printing paper, the CPU 47 calculates the difference E2−E1.
The thickness ΔD of the sheet P is calculated by −E1 (j), and the rotation amount of the motor 13 is controlled to rotate the eccentric guide shaft 7 so as to satisfy a preset relationship between the sheet thickness and the gap length. Then, the guide surface of the carriage 16 is moved in the vertical direction of the platen 1, and the gap between the print head 17 and the platen 1 is adjusted to a value optimal for the thickness ΔD of the printing paper (k).

FIG. 6 shows a second embodiment of the present invention,
Reference numeral 50 in the figure denotes a sheet thickness detection mechanism, and a light shielding plate 51 attached to the rear end of the print sheet thickness detection lever 28 as shown in FIG.
And a displacement detector 53 composed of a light-emitting element 52 and a light-receiving element 53 which are disposed to face each other.

FIG. 7 shows an embodiment of a measuring circuit for detecting a sheet thickness based on a signal from the above-mentioned displacement detector. In the drawing, reference numeral 53 denotes a light-receiving element constituting a displacement detector 54,
The output is connected to a voltage adjustment circuit 56 via a resistor 55, and is input to an operational amplifier 59 described later via a buffer amplifier 58.

Reference numeral 59 denotes the above-described operational amplifier. A signal from the buffer amplifier 58 is input to the non-inverting input terminal, and a variable resistor 60 for adjusting the inclination of the output signal, that is, for adjusting the span, is provided between the operational amplifier and the output terminal. The zero-point adjustment voltage from the reference voltage generator 61 is input to the inverted input terminal.

Reference numeral 62 denotes a light amount detection circuit comprising an operational amplifier. A signal from the buffer amplifier 58 is input to a non-inverting input terminal, and a signal from the reference illuminance setting device 63 is input to an inverting input terminal. Reference numeral 64 denotes a time constant setting circuit, which includes a high resistance 65 and a capacitor 66.
A series circuit consisting of a main time constant setting section consisting of a low resistance 67 having a resistance value approximately two digits smaller than the resistance 65 and a diode 68 conducting when the output of the light quantity detection circuit 62 is inverted is connected to a high resistance 65
In parallel, the light emitting element output adjustment circuit 69 described later is deactivated during the paper thickness detection operation, and after the paper thickness measurement is completed, when the detection lever 28 returns, the voltage quickly recovers to the initial voltage value. Then, the following measurement operation can be performed.

Reference numeral 69 denotes a light emitting element output adjusting circuit, which controls a transistor 70 based on a signal from a light amount detecting circuit 62 to emit light.
The reference current value of the light-receiving-side transistor 53 is made constant by adjusting the current flowing through the transistor 52.

Next, the operation of the thus configured device will be described.

[Initial Adjustment] At the stage when the assembly is completed, the solenoid 30 is urged to contact the platen 1 with the contact portion 34 of the sheet thickness detection lever 28 for a short time, for example, 25 milliseconds, to detect displacement. The minimum amount of light from the light emitting element 52 of the detector 54 is incident on the light receiving element 53. Light intensity adjustment circuit so that the sensor output at this time becomes the set value
63 is set, and the zero point adjusting circuit 61 is adjusted so that the output signal at this time becomes a predetermined value.

Next, the eccentric guide shaft 7 is rotated so that the gap between the platen 1 and the print head 17 or the carriage 16 becomes a reference value using a gauge or the like. In this state, the photo sensor 15 and the position detection plate 14 are moved relatively to
17 is adjusted to a predetermined gap length with respect to the surface of the platen 1 (FIG. 1), and this is set as a reference position.

Next, with the specified thickness of paper inserted,
30 is urged to pull the sheet thickness detection lever 28, and the contact portion 34 at the tip of the lever is brought into contact with the surface of the sheet having a specified thickness. As a result, the light-shielding plate 51 moves in accordance with the distance of the contact portion 34 of the lever 28 to the surface of the paper having the specified thickness. Input to the light receiving element 53 of 54. At this stage, the resistance for the span adjustment is adjusted so that an output signal corresponding to the specified thickness of the paper is output.
Set 61.

[Platen gap adjustment operation] When the printer is turned on to perform printing, the motor 13
Operates to rotate the eccentric guide shaft 7 to move the carriage 17 perpendicularly to the surface of the platen 1. In this way, when the print head 17 moves to the position where the reference gap length Gs is reached with respect to the platen surface, the reference position detection plate 14
Reaches the set reference position, a signal is output from the photo sensor 15, and the rotation of the motor 13 stops.

In this state, when the printing paper is inserted along the paper guide 25, the detection lever 26 is depressed and a paper detection signal is output from the paper detector 27, so that the CPU 72 operates the printing paper feed motor 2 to perform printing. The paper P is moved to the initial printing position.

When printing paper is set in the initial printing position,
2 momentarily excites the solenoid 30, and presses the contact portion 34 of the detection lever 28 against the platen 1 via the printing paper P in a short time, for example, only 25 milliseconds. With this, the light shielding plate
Numeral 51 stops in a state in which it rises by an amount corresponding to the thickness ΔD of the printing paper as compared with the time of the maximum light shielding, and a signal proportional to the paper thickness is output from the light receiving element 53.

By the way, in this case, since the light amount changes in the increasing direction, the diode 68 of the time constant setting circuit 64 maintains the non-conductive state. As a result, the time constant setting circuit 64 does not output a signal due to the output change from the light amount detection circuit 62 to the adjustment circuit 69 at least during the measurement period.
The output light of 52 does not change and does not interfere with the sheet thickness detection operation.

On the other hand, the signal from the buffer amplifier 58 is
Is converted to a sheet thickness by the CPU and input to the CPU 72. CPU72,
By rotating the motor 13, a platen gap that matches the sheet thickness is set.

When the sheet thickness measurement operation for one sheet is completed and the light shielding plate 51 retreats from the optical path of the displacement detector 54, the light amount detection circuit
Since the output of 62 changes in the opposite direction to that during the paper thickness measuring operation, the diode 68 of the time constant circuit 64 conducts, and the time constant is switched to a small time constant by the low resistance 67 and the capacitor 66.

In this way, when the output level of the light receiving element 53 decreases due to the fluctuation of the power supply voltage or the deterioration of the light emitting element 52 and the light receiving element 53 in a state where the sheet thickness is not measured, the light amount detecting circuit 62 The adjustment circuit 69 and the transistor 70 are operated to adjust the current to the light-emitting element 52 so as to match the set value of. Thereby, the element 5
The output from the light receiving element 53 is maintained at a constant level irrespective of the deterioration of the elements 2, 53, etc., and therefore, it is possible to detect the sheet thickness with high accuracy irrespective of the deterioration of the elements.

In this embodiment, one measurement is performed for one print sheet. However, the lever member is intermittently operated plural times, and the platen gap is adjusted based on the average value. The same effect can be obtained by measuring only the first sheet of paper at the initial stage of printing and adjusting the platen gap based on the measured value.
it is obvious.

(Effects) As described above, according to the present invention, the carriage is guided in parallel with the platen, and the carriage is provided with the carriage guide shaft for adjusting the relative gap with the platen. A lever member which is pivotally supported by a shaft and one end of which can contact the platen and is normally urged to be separated from the platen, and a displacement amount of the other end of the lever member which is provided on the base and is detected. The displacement detecting means and the means for controlling the carriage guide shaft by a signal from the displacement detecting means are provided, so that the amount of displacement transmitted to the displacement detecting means by adjusting the rotation fulcrum of the lever is suitable for the displacement detecting means. The thickness of the paper can be measured with high accuracy by measuring the paper thickness based on the base on which the platen is mounted, and the platen gap adjustment reliability and adjustment accuracy Can be improved.

In addition, since the sheet thickness detecting means is provided on the base having a large area that can be installed as compared with the carriage, the structure and the mounting operation can be simplified without the need for unreasonable miniaturization of the sheet thickness detecting means.

[Brief description of the drawings]

FIG. 1 is a plan view showing a main part of a printer to which the present invention is applied, FIG. 2 is a sectional view of the same device, FIG. 3 is a side view showing an embodiment of a printing paper thickness detecting mechanism, FIG. FIG. 5 is a block diagram showing an embodiment of a control circuit, FIG. 5 is a flowchart showing the operation of the above-described apparatus, FIG. 6 is a cross-sectional view showing a main part of a printer using another paper thickness detecting mechanism of the present invention, FIG. 7 is a side view showing a main part of a sheet thickness detecting mechanism in the apparatus shown in FIG. 6,
And FIG. 8 is a circuit diagram showing an embodiment of an operation circuit for driving the above device. 1 Platen 2 Paper feed motor 7 Eccentric guide shaft 16 Carriage 17 Print head 28 Paper thickness detection lever 30 Solenoid 33 Base

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 25/308

Claims (3)

(57) [Claims] A carriage that guides the carriage in parallel with the platen and that has a carriage guide shaft for adjusting a relative gap between the carriage and the platen, the carriage being guided by a shaft provided on the base; A lever member one end of which can be brought into contact with the platen and is normally urged to be separated from the platen; and a displacement detecting means provided on the base for detecting a displacement amount of the other end of the lever member. And a means for controlling the carriage guide shaft by a signal from the displacement detecting means. 2. The automatic platen gap adjusting device according to claim 1, wherein said displacement detecting means comprises a pressure-sensitive element. 3. The apparatus according to claim 1, wherein said displacement detecting means comprises a light emitting element and a light receiving element.